The invention relates to an optical-electromechanical transducer to monitor workpiece motion relative to the grip surface of a robot manipulator.
The sensor assembly of the instant invention is an improvement over the "Manipulator with Electro-Mechanical Transducer Means" disclosed in U.S. Pat. No. 3,171,549 issued Mar. 2, 1965, and the "Material Handling Apparatus" disclosed in U.S. Pat. No. 3,904,234 issued Sept. 9, 1975. While a slip sensor constructed in accordance with the teachings of these patents serves a useful purpose, it is not suitable for use in applications demanding decreased transducer assembly size and weight, increased sensitivity, and increased resistance to failure upon introduction of minute foreign particles into the sensor environment.
Specifically, the sensor disclosed in the "549" patent comprises a large number of elements, including a piston encompassing a plurality of solid contiguously coupled spheres, substantially increasing the overall size and weight of the assembly. The diameter of both driving and driven spheres must be small in comparison to the overall size of the sensor assembly, and, hence, the use of larger, more sensitive spheres is prohibited. Moreover, the sensor employs a high-rate spring to force engagement of these adjacent spheres, as the low coefficient of friction incident to the metal-to-metal sphere contact requires greater normal force in order to produce adequate proportional rotational response of the driven sphere in relation to the driving sphere. The use of a high-rate spring additionally produces greater frictional contact between the spheres and their bearing surfaces, producing a greater resistance to rotation, thereby reducing transducer sensitivity. The introduction of foreign particulate into the transducer environment exacerbates this frictional contact, as the surface of the driving sphere will carry the particles inside the transducer assembly, causing seizing of the assembly and reducing transducer sensitivity, reliability and responsiveness.
The "234" patent teaches an assembly comprising a light source, a light detector and a movable vane or shutter placed between the light source and light detector, with the vane's position varying proportionately with the amount of workpiece displacement. However, this "shutter technique" cannot accommodate a spherical rotatable member having a continuous, nonperforated surface, and is therefore not suitable for applications requiring the sensing of planar, as opposed to linear, slip in the absence of a second, orthogonally-oriented linear slip sensor.